Orthodontic brackets made of crystalline alumina (sapphire) have been proposed. Such brackets are described in U.S. patent application Ser. No. 743,851, filed on June 12, 1985 (now U.S. Pat. No. 4,639,218), assigned to the same assignee as this application.
Orthodontic brackets are usually bonded directly to teeth with an acrylic cement. It has proven to be difficult to obtain sufficient bond strength between acrylic cements and crystalline alumina brackets to ensure that such brackets will not come off during normal use.
One approach to improving the bond strength between crystalline alumina orthodontic brackets and acrylic cements is described in U.S. Pat. No. 4,595,598 and U.S. Pat. No. 4,681,538, parent applications to this application. That approach was to form a thin, adherent coating of a siliceous material such as silica on the surface of the alumina. The silica coating increases the bond strength of the alumina to acrylic cements, especially when primed with a silane coupling agent. The specific methods for forming the siliceous coating on the alumina that are disclosed in the said parent applications include cathode sputtering, plasma deposition, and electron beam evaporation.
This invention provides an improved method for forming a thin, adherent coating of a siliceous material on the surface of alumina, preferably crystalline alumina, to thereby enhance the bond strength to acrylic adhesive cements, and is particularly directed to an improved method for applying alumina orthodontic brackets to the teeth of a patient utilizing alumina brackets wherein the tooth contacting surface has a thin, adherent coating of a siliceous material produced by the method of this invention.